Implanting an electrode array against the spinal cord inside the dura for stimulating the spinal cord and treating pain

ABSTRACT

A method for treating intractable pain via electrical stimulation of the spinal cord. Remote, non-contact stimulation of a selected region of spinal cord is achieved by placement of a transceiver patch directly on the surface of that region of spinal cord, with said patch optionally being inductively coupled to a transmitter patch of similar size on either the outer or inner wall of the dura surrounding that region of the spinal cord. By inductively exchanging electrical power and signals between said transmitter and transceiver patches, and by carrying out the necessary electronic and stimulus signal distribution functions on the transceiver patch, the targeted dorsal column axons can be stimulated without the unintended stray stimulation of nearby dorsal rootlets. Novel configurations of a pliable surface-sheath and clamp or dentate ligament attachment features which realize undamaging attachment of the patch to the spinal cord are described.

CROSS REFERENCE TO RELATED APPLICATION DATA

This application is a continuation application of U.S. patentapplication Ser. No. 13/885,157, filed on Jan. 6, 2014, and patented asU.S. Pat. No. 9,364,660 on Jun. 14, 2016, which is the U.S. NationalStage of International Application PCT/US2011/060462, filed on Nov. 11,2011, which claims the benefit of U.S. Provisional Application No.61/412,651, filed Nov. 11, 2010; the full discloses of which areincorporated herein by reference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to medical devices and methods.More particularly, the present invention relates to electrode structuresand systems for delivering electrical pulses directly to the spinal cordof a patient to block pain and for other purposes.

The use of spinal cord stimulation (SCS) to relieve intractable painsymptoms originated in the 1960's along with emerging theories of theneural basis of pain perception and the pathophysiology of chronic paindisorders. Results from experimental animal studies demonstrated theexistence of neural pathways that originate within the brain and projectaxons through the spinal cord that eventually terminate at spinal cordlevels where pain signals from the peripheral nervous system enter thecentral nervous system. These pathways are postulated to play a role inthe ‘top-down’ modulation of pain perception. Human SCS studies wereinitiated based on the theory that by using electrical stimulation toartificially activate descending pathways within the dorsal column ofthe spinal cord, the processing of pain related signals below thestimulation site could be attenuated, blocked or otherwise modulated.

Although the specific neural mechanisms that underlie the clinicalefficacy of this treatment remain poorly understood, there is nowabundant clinical evidence that SCS is capable of providing sustainedpain relief to select patients with intractable chronic pain. The mostimportant limitation of this treatment method is that a high percentageof patients implanted with an SCS system or device may experience onlymarginal improvement, or no improvement, in their pain symptoms.Treatment success rates of 50% or less are frequently reported withknown SCS systems.

The neural mechanisms that mediate the clinical effects of SCS arecomplex and likely involve activation of multiple ascending anddescending neural pathways within the spinal cord. Based on empiricclinical evidence, a number of treatment concepts have emerged to guideSCS strategies. In general, electrical stimulation will evoke sensoryperceptions in the painful area of the body in order for the treatmentto be effective. To accomplish this, the region within the dorsal columnof the spinal cord that contains axons that are functionally related tothe painful body area must be activated. Dorsal column axons aresomatotopically organized, meaning that the axons that are functionallyrelated to a particular body area are positioned in close proximity toeach other, and there is an orderly anatomical pattern of organizationwithin the spinal cord for the different groups of axons linked todifferent body areas. In the cervical spinal cord, for example, dorsalcolumn axons functionally linked to the back region may be relativelyclose to the midline of the spinal cord, and axons linked to the armsare positioned relatively more laterally.

Adverse effects of electrical stimulation can result from unintendedactivation of non-targeted neural structures. When the dorsal nerverootlets are activated, for example, discomfort can result. Theeffectiveness of SCS treatment is generally dependent on the capacity ofthe device to selectively activate targeted axons within a specificsub-region of the dorsal column, without activating the nearby dorsalrootlets. This concept is incorporated into researchers use of the termtherapeutic range to describe the range of stimulus intensities that areabove perceptual threshold (i.e. effectiveness threshold) but below thediscomfort threshold, beyond which stimulation effects are no longertolerated by the patient. The ideal SCS device will be capable ofefficiently and safely delivering highly focused electrical stimuli tothe targeted sub-region of the dorsal column without activating nearbystructures. The electrode contact should be positioned as close to thetargeted-axons as possible and the resulting volumetric pattern oftissue activation should tightly conform to the anatomy of the targetedneural pathway.

The spinal cord is cylindrically shaped and positioned centrally withinthe spinal canal. The spinal canal is lined by a dural membrane andcontains cerebrospinal fluid (CSF) that surrounds the spinal cord andfills the region between the outside surface of the spinal cord and theinside surface of the dural membrane. This CSF-filled space plays acritical role in normal spinal cord biomechanics and is an importantfactor that should be considered when performing spinal surgery. Duringnormal movements, such as flexion and extension of the body, the spinalcord moves within the spinal canal, altering its position relative tothe dural lining of the spinal canal. The volume of CSF surrounding thespinal cord serves as a frictionless buffer during these movements. Insome pathological conditions (e.g. tethered cord syndrome) this normalmotion of the spinal cord is impeded by tissue attachments bridging thespace between the spinal cord and the dural lining, resulting indysfunction of the spinal cord. In other pathological conditions, atissue barrier forms within the spinal canal (e.g. following trauma orinfection) that disrupts the normal flow of CSF over the surface of thespinal cord. In this setting CSF may accumulate within the substance ofthe spinal cord to form a syrinx and cause neurological dysfunction.

The dural listing of the spinal canal should be managed with particularcare during spinal surgery. If a detect is created in this lining, a CSFfistula may develop which increases the risk of a wound complication(infection or dehiscence) and may cause the patient to experiencedisabling positional headaches. In order to access the spinal corditself, the dural membrane should be opened surgically and this isperformed in a manner that allows the surgeon to achieve a ‘water-tight’closure at the completion of the operation. Typically this involvessharply incising the dura over the dorsal aspect of the spinal canal, alocation that is readily accessible and well visualized during surgery.Later the dura is re-approximated by suturing together the well definedcut margins of the fibrous membrane. This closure technique is performedin a manner that preserves the CSF filled space separating the dura fromthe spinal cord, thus preventing mechanical constriction, or tethering,at the surgical site.

These anatomical and surgical considerations have impacted the evolutionof a wide range of operative procedures, including spinal cordstimulator surgery. When the design intent is to minimize the risk ofsurgical complications, the optimal strategy is to entirely avoidopening the dural membrane and place the implant outside of the dura(extra-dural procedure). If the spinal cord must be accessed directly(intra-dural procedure) the operation should be designed in a mannerthat prevents CSF fistula formation, mechanical tethering of the spinalcord to the dura, or physical obstruction of the CSF filled spacesurrounding the spinal cord.

There are limitations in the performance characteristics of the priorart. One such limitation is the following. Existing SCS devices deliverelectrical stimuli through electrodes placed outside of the fibrouslining of the spinal canal (dura). This results in inefficient andpoorly localized patterns of spinal cord activation due to theelectrical shunting effect of cerebrospinal fluid that fills the spaceseparating the dural lining and the spinal cord. This inability toselectively activate targeted regions of the spinal cord is thought tobe an important contributing factor to the significant incidence ofsub-optimal or poor treatment outcomes with existing SCS devices.Despite these limitations large numbers of patients are implanted. Thesize of the SCS market attests to the large scope of this public healthproblem and the fact that under certain circumstances, electricalactivation of the spinal cord provides pain relief for patients who havefailed all other treatment modalities.

A further limitation of the prior art arises in the nature of certaintethered forms of spinal cord stimulators. When SCS electrodes werefirst placed in human subjects, most were implanted on the surface ofthe dura, but in some instances the dura was opened and electrodes wereplaced directly on the surface (intradural) of the spinal cord(Gildenberg 2006, Long 1977, Long 1998, Shealy et al. 1970). The wiresfrom electrodes placed directly on the spinal cord passed through thedura, thus mechanically tethering the electrode to the dura. Theelectrodes were constructed of conventional conductive and insultingmaterials, were bulky, and had a limited number of contacts throughwhich stimuli could be delivered. The locations of the contacts relativeto targeted and near-targeted neural structures were difficult tocontrol and could not be adjusted following the implantation surgery.Because of these factors, and the increased risks associated withopening the dura, at the time there was no obvious therapeutic advantageto the intradural approach. The use of intradural stimulating electrodeswas eventually discontinued and currently all SCS devices use extraduralstimulating electrodes.

Still another limitation of the prior art arises in terms of thetreatment efficacy. There are two broad classes of extraduralstimulation electrodes. One type can be placed percutaneously through aneedle into the epidural space. These electrodes have smallcylindrically shaped contacts positioned along the shaft of a flexiblelinear electrode array. They are used either for minimally invasivetesting of stimulation effects prior to implantation surgery, or as thedevice that is permanently implanted. The other type of extraduralelectrode is placed during an open surgical procedure and consists of aflat array of multiple electrode contacts positioned over the exposeddural surface. An experienced practitioner is capable of implantingthese extradural electrodes with a high degree of safety. However, thecurrent SCS devices have suboptimal treatment efficacy. We hypothesizethat this shortcoming is due in large part to the inability ofextradural electrodes to selectively activate the targeted sub-region ofthe dorsal column of the spinal cord. By placing devices outside of thedura because of safety considerations, an intrinsic disadvantage isincurred in terms of therapeutic efficacy. The presence of a CSF filledspace between an extradural stimulating electrode and the spinal cordprofoundly degrades the ability of the device to create a volume ofelectrical activation that selectively encompasses the targetedsub-region of the spinal cord. This results from the conductiveproperties of CSF. CSF is a far more efficient electrical conductor thanany other tissue in the spine (Holsheimer 1998). When an electricalstimulus delivered by an extradural electrode traverses the dura andenters the CSF-filled space between the dura and the spinal cord, alarge fraction of the stimulus is electrically ‘shunted’ diffuselywithin this CSF filled space. Researchers estimate that extraduralstimulation results in the spinal cord receiving less than 10% of thedelivered stimulus. The stimulus effect penetrates the spinal cord to adistance of 0.25 mm or less and the broad volumetric pattern encompassesboth targeted (i.e. dorsal column) and non-targeted (i.e. dorsalrootlets) neural structures (He et al. 1994, Holsheimer 1998, Holsheimer2002, Holsheimer et al. 2007).

The clinical importance of these limitations of the prior art arereflected in the numerous efforts made by device manufactures tomitigate the problems. These include the development of spatiallydistributed multi-contact extradural arrays and stimulation protocolsthat enable delivery of electrical charge distributions over widelyvariable anatomical patterns. This strategy allows the physician toadjust the anatomical location of maximal stimulation on the duralsurface, but the presence of CSF shunting continues to markedlyattenuate the stimulation effects within the spinal cord. Clinicianshave also used a strategy of placing multiple cylindrical electrodeswithin the extradural space tor the purpose of mechanically reducing thesize of the CSF-filled space and displacing the electrode contacts to aposition closer to the spinal cord (Holsheimer et al. 2007). A devicemodification recently introduced by one of the largest manufacturer ofSCS devices seeks to address problems associated with movement of thespinal cord within the CSF-filled spinal canal that occurs when patientschange position. These positional changes after the spatial relationshipbetween an extradural electrical source and the spinal cord, and thepattern of tissue activation. The new device senses patient position andautomatically adjusts stimulus parameters for the purpose of achievingstable therapeutic effects. As with all other SCS design changesintroduced to-date, the addition of a position sensor does not addressthe fundamental problem of CSF shunting of the electrical stimulus.

BRIEF SUMMARY Of THE INVENTION

The present invention addresses a major public health problem: medicallyintractable chronic pain. Specifically, embodiments of the inventionprovide devices and methods for providing effective symptomatic relieffor patients suffering from chronic pain syndromes resulting from injuryor disease affecting musculoskeletal, peripheral nerve, and other organsystems of the body. More specifically, embodiments of the inventionprovide surgically implanted devices adapted for electrical stimulationof tissues of the nervous system. Still more specifically, someexemplary embodiments of the present invention provide devices andmethods for direct electrical stimulation of the spinal cord, optionallyby wireless inductive coupling of signals from an electrical signalgenerator which may be located on the dura surrounding the spinal cordto an electrode assembly adapted to be implanted directly on the surfaceof the spinal cord, thus obviating the need for wires, leads or othersuch connections disposed through the dura. Many embodiments of thespinal cord stimulation devices described herein may be supported inengagement with the spinal cord by attaching features of the device todentate ligaments extending laterally between the spinal cord and thesurrounding dura, with either wireless or wired coupling to a signalgenerator disposed outside the dura. Most embodiments of the devices andmethods of the present invention will electrically stimulate welldefined, circumscribed sub-regions of the spinal cord with both a degreeof spatial precision and a therapeutic level of electrical intensitythat cannot be achieved using existing spinal cord stimulation (SCS)devices. In specific embodiments, the electrode assemblies compriseflexible electronic microcircuitry, optionally with thin-film electrodearrays, at least the latter of which are configured to be in directphysical contact with the surface of the spinal cord. The implantedelectrode assemblies may be remotely powered and controlled (with nophysical connections to or through the dural lining of the spinalcanal), or may have a plurality of conductors extending through thedura, to selectively activate targeted regions of the spinal cord withextreme precision and the requisite electrical intensity.

The devices and methods of the subject invention address the mostimportant deficiencies of current SCS devices in the prior art byincorporating the following design features into the device:

1) the electrical stimuli are delivered directly to the spinal cord;

2) a dense array of electrode contacts enables delivery of highlylocalized, spatio-temporally synchronized (could also multi-plex,alternating stimuli between various electrode montages), andpositionally selective electrical stimuli to any targeted sub-region ofthe spinal cord;

3) the device does not mechanically tether or form a physical connectionbetween the spinal cord and dura that significantly alters the naturalsupport and flexibility provided by the dentate ligaments;

4) the implantable electrode assembly has as ultra-thin physical profilethat does not obstruct or alter CSF flow patients around the spinalcord;

5) the contact forces between the device and the spinal cord are stableand unvarying, and hence patient movement does not affect these contactproperties, which results in optimal electrical coupling betweenelectrode contacts and spinal cord tissue;

6) the compliant nature of the device materials accommodates pulsationsof the spinal cord without any harmful reactive or dissipativecounter-forces;

7) the materials used to construct the device are highly resistant toelectronic or structural failure with break rates that may be lower than(or similar to) existing devices, optionally using materials that arealready included in stimulation implant devices or novel proprietarymaterials;

8) the surgical procedure (laminectomy) used to implant the device iswell established and safe, and when performed by skilled practitioners,the risk of CSF fistula formation with this procedure will not differsignificantly from complication rates associated with current surgicalimplantation procedures used to implant extradural electrode arrays;

9) the increased duration of implantation surgery, compared to currentprocedure times for surgical implantation of extradural SCS devices,will not exceed 30 minutes; and

10) the manufacturing cost of the new device may (in at least someembodiments) be less than that for existing devices (particularly forthe ‘wired’ I-Patch).

The electrode assembly, hereinafter referred to as the Iowa-Patch(I-Patch) fulfills at least some of these design criteria, and iscomposed of advanced flexible electronics technologies. The electronicelements of the I-Patch are imbedded in (optionally being between layersof) a flexible polymeric or elastomeric “patch” or substrate. Electricalstimuli are delivered via an array of contacts that, when in position,can provide axial and circumferential coverage directly onto the lateraland/or dorsal surfaces of the spinal cord. Precisely localized patternsof spinal cord stimuli are achieved by selectively activating thepreferred combinations of electrode contacts in any desired,programmable spatio-temporal sequences. In one embodiment, flexiblepolymer ‘arms’ of the device are optionally contoured to provide acontinuous, gentle inward “capture” force that insures an optimalelectrical interface between the device contacts and spinal cord tissue,while avoiding mechanical constriction of the spinal cord.

In one embodiment, the dorsal (outer) surface of the I-Patch containsembedded microcircuitry that implements stimulus delivery algorithms.Circuit elements may include an RF antenna that receives power andcontrol commands from an intra- or extradural device described below, aswell as other circuit elements that generate and route electricalstimuli to the appropriate electrode contacts. The self-containedI-Patch may have no mechanical or other physical connection with anyother element of the SCS system. Alternatively, small gauge, flexibleconductors may extend between the dura and the spinal cord along adentate ligament, to which said conductors may be affixed, saidligaments being the structures of the body that support the spinal cordwithin the dura. Hence, when the device is in place there is nosubstantive spinal cord tethering or disruption of CSF flow dynamicsaround the spinal cord. All the device surfaces, with the exception ofthe electrode contacts, are either composed of or coated with abiocompatible insulating material, such as medical grade silicone, andthe finished intradural device is very thin, on the order of (andtypically being) 0.5 mm or less.

In one embodiment, the I-Patch is Inserted surgically by performing alaminectomy, creating a mid-line dorsal durotomy, inserting the deviceonto the spinal cords and then suturing the dura closed. Because, afterimplantation of some embodiments, no portion of the device penetratesthe dura, and the dura is opened and closed in an optimally controlledmanner, the risk of CSF fistula formation will be low.

A power and control signal transfer circuit assembly, constructed withina thin, hermetic encapsulation, is positioned either in the extraduralspace (over an exterior surface of the dura) or on the inside surface ofthe dural membrane, in either case overlying the I-Patch implant. Thistransfer circuit assembly generates power and command signals that aretransmitted across the CSF filled space surrounding the spinal cord, andam received by the I-Patch, either wirelessly or along a conductor. Thepower and/or signal circuit assembly (or components thereof) may beincorporated in the main power supply battery and control circuitassembly in wired embodiments of the I-Patch. The extradural device issecured in place using sutures and includes flexible electrical leadsthat are connected to a power supply battery and control circuitassembly that is implanted in the subcutaneous tissue of the patient'sabdominal wall. The entire system can be controlled via wirelesscommands that employ technologies similar to those used in standard SCSdevices. The flexible microelectronics materials used are extremelyrobust and resistant to breakage. Such circuits have been usedextensively in harsh conditions ranging from deep space (rockets andsatellites) to consumer use of folding hand-held cell phones.

The I-Patch system specifically targets one aspect of SCS deviceperformance and value: treatment efficacy. Because of improvements Inthe ability to precisely activate targeted sub-regions of the spinalcord, the I-Patch system will significantly improve the treatmentefficacy when compared to current devices.

The I-Patch system can be used for all spinal cord stimulationapplications, including treatment of patients with Parkinson's disease.Spinal Cord Injury, and Congestive Heart Failure. While usuallyemploying surface contact electrodes, the system can also be modified toincorporate penetrating microelectrodes that emanate from the I-Patchplatform and enable delivery of electrical stimuli to sub-surface neuraltargets. Such a system can be used not only in the spinal cord, but alsoin the brain and other organ systems.

One skilled in the art can see that many other embodiments of means andmethods for non-contact spinal cord stimulation according to thetechnique of the invention, and other details of construction and usethereof, constitute non-inventive variations of the novel and insightfulconceptual means system, and technique which underlie the presetsinvention.

Thus, in a first specific aspect of the present invention a method fortreating pain in a patient comprises conformably postponing an electrodearray over a surface of the patient's spinal cord so that a plurality ofindividual electrodes in the array directly contact selected locationson the spinal cord. Electrical stimulation energy is then delivered in acontrolled spatio-temporal sequence to a targeted sub-region of thespinal cord to relieve pain without stimulating dorsal nerve rootlets.Typically, conformably positioning the electrode array comprisescircumscribing a structure of the array around the spinal cord, withsome embodiments circumscribing more than 180° but less than all (360°)of the spinal cord circumference. Conveniently, the circumscribing arraystructure can have an elastic C-shaped geometry which can be opened andelastically closed over the spinal cord to hold the electrode array inplace while accommodating spinal cord pulsation and other motions. Inthis way, the electrode array structure when implanted to circumscribethe spinal cord will not substantially obstruct CSF flow, thus reducingthe risk of syrinx formation. Alternative embodiments may circumscribeless than 180° of the spinal cord, with the electrodes of the arrayoptionally being disposed primarily or even entirely over the dorsalsurface of the spinal cord between left and right dentate ligaments.

In preferred aspects of the method of the present invention, theindividual electrodes will be distributed over at least points on thedorsal surfaces of the spinal cord, and optionally over the lateral andventral surfaces, so that sufficient regions of the spinal cord surfaceare contacted to permit selective actuation of the electrodes andtargeted stimulation of a variety of spinal cord anatomical sites asdescribed in more detail below. As described above, stimulation of theimplanted electrode structure on the spinal cord will optionally beachieved by wirelessly transmitting energy to the electrode array from asignal generator disposed remotely from the array. Usually, the signalgenerator will be implanted to lie either directly on the externalsurface of the dura or just underneath the internal surface of the dura,preferably directly over the implanted location of the spinal cordelectrode array. Alternatively, however, the signal generator in somecases could be more remotely located and provide for transcutaneous orother remote transmission of power and signal to the implanted spinalcord electrode array. Embodiments may include one or more flexibleconductors (such as a flex-circuit, conductor wires, or conductorcables) extending between the array structure and an implanted generatorsystem, with the conductors traversing through the dura and oftenextending along and being affixed to a dentate ligament.

In still further aspects of the present invention, an electrode arrayadapted to conform to an exterior surface of a patient's spinal cordcomprises a compliant backing having an interior surface and an exteriorsurface, where the interior surface is adapted to lie in contactdirectly over the exterior surface of the spinal cord. A plurality ofelectrodes are formed over at least a portion of the interior surface,and transceiver and control circuits are disposed on or immediatelybeneath the exterior surface of the compliant backing. The transceiver'santenna may be adapted to receive power and signals from a remote signalgenerator, as described above, while the circuitry will be able toaccept and process power and information signals from the antenna andconvert the resulting currents to nerve stimulating pulses to bedelivered by the electrodes to the spinal cord. The electrode array mayinclude a C-clamp structure adapted to resiliently circumscribe at leasta portion of the spinal cord, preferably circumscribing over 180° of thecircumference while not completely enclosing the entire circumference.

In some preferred embodiments, the electrode circuitry carried by theelectrode array will be adapted to selectively stimulate individualelectrodes in response to the external signals received by thetransceiver's antenna in order to deliver spatio-temporally selectedstimuli to targeted regions of the spinal cord. Hence, a signalgenerator or other external circuitry may be programmed to treatparticular conditions by stimulating targeted regions of the spinalcord, and such targeted stimulation will be achieved by selectivelyenergizing particular ones of the individual electrodes which are partof the electrode array. Preferred anatomical target regions within thespinal card will be chosen by the neurosurgeon and consultingneurologists and might include the thoracic, lumbar and sacral regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional diagram of selected anatomical elementsof the spinal cord.

FIG. 1A shows a cross-sectional view of the spinal cord with specificanatomical locations identified.

FIG. 2 shows a cross-sectional diagram of the results of extraduralstimulation of the spinal cord.

FIG. 3 shows an illustration of the principal electronic subsystemsresident on a wireless embodiment of the I-Patch receiver element orarray structure.

FIG. 4 shows an illustration of the underside of the I-Patch receiverelement of FIG. 3, which would be in contact with the surface of thespinal cord.

FIG. 5 shows the deployment of the I-Patch receiver device on thesurface of the spinal cord.

FIG. 6 shows a lateral view of the relative positions of the wirelessI-Patch transmitter and receiver devices, on the surfaces of the duraand spinal cord, respectively.

FIG. 7 shows a cross-sectional view of the relative positions of theI-Patch transmitter and receiver devices, on the surfaces of the duraand spinal cord, respectively.

FIG. 8 shows a schematic representation of the inductive coupling actiontaking place between the I-Patch transmitter and receiver devices.

FIG. 9 illustrates a I-Patch having penetrating electrodes for accessinginternal target regions within the spinal cord.

FIGS. 10-13 illustrate a full-circumference pliable electrode structureand method of implantation, intended to fully circumscribe the spinalcord to provide access to additional targeted regions therein.

FIGS. 14, 15, and 15A illustrate spiral and staggered electrode patchvariations according to the present invention.

FIGS. 16 and 17 illustrate an insertion device for implanting theelectrode assembly of the present invention on a spinal cord.

FIGS. 18 through 21 illustrate an intra-dural relay device fordelivering power and signals to the implanted I-Patch when implanted onthe spinal cord.

FIGS. 22 and 23 show exemplary schematic diagrams of one embodiment ofthe circuitry that might be incorporated onto the I-Patch implant

FIG. 24 shows the postulated somatotopic organization of the dorsalspinal column axons.

FIGS. 23 and 25A show a perspective view and an axial view of theanatomical arrangement of the spinal cord tissues, including thepresence of the dentate ligaments which support of the spinal cordwithin the spinal canal.

FIGS. 26 and 26A show a top down or dorsal view of an alternativeembodiment of an I-Patch supported on a dorsal surface of a spinal cordby fixation to a dentate ligament so as to support the I-Patch,respectively.

FIGS. 27 and 27A show a perspective view and a plan view of yet anotheralternative embodiment of an I-Patch configured to be supported by armsthat clamp to dentate ligaments on either side of the spinal cord.

FIGS. 28-28F illustrate a still further ‘wired’ alternative embodimentof an I-Patch secured to dentate ligaments, along with implantation ofthe device so that a lead extends along (and is attached to) one of thedentate ligaments arm is sealed where it extends through the dura.

FIG. 29 schematically illustrates en electrode extending from aninterior surface of a hacking or substrate of an array structure of theI-Patch.

FIG. 30 schematically illustrates individual electrodes flexibly mountedto a backing or substrate by a soft resilient material so as to allowthe electrode to float and inhibit sliding movement of the electrodeagainst a surface of the spinal cord during pulsation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-sectional diagram of selected anatomical elementsof the spinal cord. These include the layer of dura mater 10 thatencompasses the spinal cord SC and encloses the spinal canal, the dorsalnerve rootlets 12, the zone of cerebrospinal fluid 14 that separates theouter surface of the spinal cord from the inner surface of the dura, andthe axons 16 that would be targeted by spinal cord stimulationinstrumentation.

FIG. 1A illustrates the complex anatomical arrangement of the postulatedhuman spinal cord pathways. In the large dorsal column pathways (f.gracilis, f. cuneatus) activation of large numbers of axons that arelocated greater than 0.5 mm deep below pial surface will likely resultin broader somatotopic coverage of painful areas of the body and anincreased magnitude of pain attenuation effects. Activation of axonswithin deeply positioned dorsal mid-line structures (e.g. septomarginalf., posterior proper f.) may result in complete relief of visceral pain.Pathways positioned within the lateral and anterior regions of thespinal cord are not activated by current SCS devices. There are manypotential stimulation targets in these regions, including the posteriorand anterior spinothalamic tracts which conduct pain and temperaturesignals to the brain.

Spinal cord stimulation may also be effective in treating patients withmovement disorders (e.g. Parkinson's Disease). There are a large numberof potential motor and motor-modulation pathways throughout the humanspinal cord that may represent optimal targets for this novel clinicalapplication, e.g. lateral cerebrospinal f., rubrospinal, tectospinal f.,dorsal spinocerebellar f., ventro spinocerebellar f., all of which arebeyond the range of current SCS devices. The I-Patch system (surface andpenetrating electrode variants) will be capable of selectivelyactivating any spinal cord pathway, in any location, in a patient with afunctionally intact spinal cord. Stimulation of these sites will likelyresult in markedly improved spinal cord stimulation clinical efficacy.

FIG. 2 shows a cross-sectional diagram of the results of extraduralstimulation of the spinal cord. The standard epidural stimulatingelectrode 20 is placed on the outside of the dura, and the field itproduces is attenuated significantly by the presence of the CSF 14. Theresulting field within the spinal cord is very weak, having littleeffect on the targeted dorsal column axons, but instead causingdiscomfort tor the patient via parasitic activation of the dorsalrootlets 12.

FIG. 3 shows a conceptual illustration of the principal electronicsubsystems resident on a wireless embodiment of the I-Patch receiver orarray structure element 28. Seen there (on the left) are the turns of amicrofabricated coil 30 that is configured to serve as an RF receiverthat couples inductively to the counterpart coil on a paired transmitterelement, this enabling the I-Patch to receive power, information, andcontrol signals. Also shown (on the right) are the circuits 32constituting the control elements that regulate the size, timing anddistribution of the stimuli that act on the electrodes 34 (center).Flexible attachment arms 36 extend from either side of a central body ofthe I-Patch, with the attachment arms typically being formed at least inpart of the substrate or backing material on which circuit components 32are mounted or formed.

FIG. 4 shows an illustration of the underside of the I-Patch receiverelement, which would be in contact with the surface of the spinal cord.The electrodes 34 (center) are positioned by the neurosurgeon over theregion of spinal cord to be stimulated. The underside of thebiocompatible I-Patch is in contact with the surface of the spinal cord,and held to it by the gentle clamping action of the extension arms 36shown in the figure.

FIG. 5 shows the deployment of the I-Patch receiver device 28 on thesurface of the spinal cord SC. The extension arms 36 of the receiverdevice 28 partially encircle the body of the spinal cord SC, thus gentlyclamping the I-Patch to it. The extension arms are positioned to residebetween the dorsal rootlets 12, and not be in contact with them. Undersome circumstances a number of dorsal rootlets may be sectioned toaccommodate placement of the I-Patch.

FIG. 6 shows a lateral view of the relative positions of the I-Patchtransmitter 40 and receiver 28 devices, on the surfaces of the dura 10and spinal cord SC, respectively. The transmitter 40 and receiver 28patches are inductively coupled to each other by electromagnetic fieldsestablished through current flows in the windings on their respectivesurfaces. The strength of the coupling can be adjusted by regulation ofthe strength of the current flow. In this way, power, information, andcontrol signals can span the zone of CSF resident between the insidesurface of the dura and the outer surface of the spinal cord.

FIG. 7 shows a cross-sectional view of the relative positions of theI-Patch transmitter 40 and receiver 28 devices, on the surface of thedura 10 and surface S of the spinal cord SC, respectively. Bypositioning the very thin I-Patch receiver directly on the surface S ofthe spinal cord SC, it is possible to drive the electrodes such that thestimuli fields penetrate through the whole treatment zone of interestand are not attenuated by the CSF. Also, this type of stimulus fieldconcentration insures that there is no parasitic excitation of thedorsal rootlets, with the resulting associated pain. To a roughapproximation, the instantaneous electric field, E, within thestimulation stone will be given by E=σ/2κ∈₀ where σ is the surfacecharge density created at the electrode's surface, κ∈₀ is the product ofthe dielectric constant of the spinal cord substrate and thepermittivity of free space. End effects associated with the geometry ofeach individual stimulus electrode will modify this simple model, aswill superposition of the fields due to the simultaneous activation ofone or more neighboring electrodes.

FIG. 8 shows a schematic representation of the inductive coupling actiontaking place between the I-Patch transmitter 40 and receiver 28 devices.As seen there, the power, information, and control signals generated bythe transmitter device on the dura side of the system are inductivelycoupled across the CSF fluid to the receiver device, where they areoperated on by the on-board controller, and stimuli signals aredistributed to the electrodes. The inductive coupling action is governedby the mutual inductance between the two sets of windings.

The optional ‘wireless’ design of the I-Patch system is a very importantdesign aspect of some embodiments. However, alternative embodimentsemploy ‘wired’ versions of I-Patch devices that are safe and effective,as described below. Embodiments of these wired devices may have higherrates of mechanical failure and be associated with increased risks ofcomplications compared to a wireless I-Patch version, but would functionand potentially be useful for certain applications.

The I-Patch can deliver electrical stimuli to regions of the spinal cordthat are targeted by current SCS devices. This is accomplished bypositioning electrodes on the pial surface of the spinal cord. It ishighly likely that therapeutic effects can also be achieved byselectively stimulating circumscribed sub-regions of the spinal cordpositioned deep to the pial surface. In fact, the spatio-temporallyselected electrical stimulation of certain structures within the centralregions of the spinal cord may result in therapeutic benefits thatcannot be achieved with surface stimulation. A broad range of clinicalapplications, beyond the currently targeted chronic pain treatments,will likely be available via placement of chronic penetrating I-Patchelectrodes (e.g. activation of motor pathways to treat patients withmovement disorders or paralysis).

The penetrating electrode I-Patch 50 is illustrated in FIG. 9.Multi-contact penetrating electrodes 52 extend from the I-Patch mainassembly 54. The interface between the main assembly and penetratingelectrode shaft may be held rigid (at least during implantation),allowing the surgeon to insert the penetrating electrode into the spinalcord by advancing the I-Patch device toward the dorsal spinal cordsurface using the I-Patch Applier. Once the main assembly is in contactwith the surface of the spinal cord, the flexible I-Patch attachmentarms are optionally released restating in a stable attachment betweenthe spinal cord and the electrode assembly. In some embodiments, theelectrodes may, after implantation, be supported relative to each otherand the substrate or backing of the I-Patch with resiliently flexiblematerials, thereby allowing the overall array of electrodes toaccommodate pulsation and the like. Suitable resilient flexible supportof the electrodes may be provided using a flexible material spanningbetween the electrode and walls of an aperture through the substrate,with the flexible material optionally comprising a separate layer bondedto the substrate, material insert molded within apertures through thesubstrate, or the like. Electrical stimuli are delivered through selectpenetrating electrode contacts using control circuitry embedded in theI-Patch main assembly. The geometric contour of electrical stimulationeffects surrounding a given penetrating electrode contact is shaped bythe selection of other I-Patch surface and penetrating electrodecontacts that are incorporated into bi-polar, or multi-polar stimulationmontages.

Clinical applications that target neural pathways on ventrally locatedsurface structures of the spinal cord that may be targeted with amalleable full-circumference I-Patch prototype as illustrated in FIG.10.

In contrast to the I-Patch designs with elastic C-clamps, as describedabove, the device 60 of FIG. 10 is fully pliable and has no ‘memory’ ofthe curvature of the spinal cord. A dense array of electrode contacts 62is imbedded in a flexible band 64 extending from a body of the deviceand capable of fully circumscribing the spinal cord. This flexible band64 is inserted in the space between the dura and the spinal cord andgently advanced until the leading edge is visible on the opposite sideof the spinal cord (FIGS. 11 and 12). The leading edge of the electrodehand is then crimped, pinned or otherwise seemed to the main assembly ofthe I-Patch device (FIG. 13) by a crimping device 66 or the like.

The pliable band achieves the objective of positioning electrodecontacts in an un-interrupted linear array covering the entirecircumference of the spinal cord. The drawbacks of this design are thatthe insertion technique is more difficult and associated with increasedrisks compared to the standard I-Patch. When advancing the electrodeband around the circumference of the spinal cord there will be a smallrisk of injuring nerve roots or causing a hemorrhage. Also, themechanical contact, and thus electrical coupling, achieved between theelectrodes and spinal cord surface will be less optimal than with thestandard I-Patch prototype. The full-circumference band cannot beattached so tightly that it impedes spinal cord pulsation; this wouldresult in injury to the neural tissue. Conversely, a ‘loose fitting’circumferential band will not exert the optimal inward forces on theelectrode contact and thus allow spinal fluid to flow between theelectrode contact and the pial surface resulting its sub-optimalelectrical coupling. One potential design variant would involve havingthe electrode contacts protrude from the flexible band, allowing torfirm contact between electrodes and the pial surface, but also gapsbetween the pial surface and the non-electrode bearing portions of theflexible arm. These gaps would accommodate pulsatile spinal cordexpansion and contraction.

Alternative patch designs with reduced spinal cord compression andimproved accommodation of spinal cord pulsations are illustrated inFIGS. 14 and 15. The devices of FIGS. 14, 15, and 15A have incompletering configuration and elastic properties that enable the devices togently expand and contract along with the spinal cord. The I-Patchvariant 70 of FIG. 14 has spiral attachment arms 72, and the staggered IPatch variant 80 of FIGS. 15 and 15A has staggered arms 82.

The devices of FIGS. 14 and 15 further reduce the degree of mechanicalconstriction in a given cross-sectional portion of the spinal cord. Thenet effect of gently exerting inward forces on the device to maintaincontact with the spinal cord is achieved by ‘staggering’ the attachmentarms, or by using ‘spiral’ configured attachment arms.

An I-Patch applier (IPA) 90 is illustrated in FIGS. 16 and 17. The IPA90 will preferably enable the surgeon to maintain a rigid, butreversible attachment to the I-Patch main assembly of receiver 28. Whilemaintaining a rigid attachment of the I-Patch with a main assembly ofthe IPA 90, the surgeon will have the ability to adjust the position ofthe I-Patch's pliable attachment arms in an incremental, preciselycontrolled, and reversible manner. After the I-Patch is placed on thesurface of the spinal cord, and the flexible attachment arms are intheir final position, the IPA allows the surgeon to safely andefficiently detach the I-Patch from the IPA.

The IPA 90 can be used as a hand-held device, or attached to anintra-operative mechanical advancer device. The surgeon controls theposition of the IPA fey controlling the insertion device rod 92 (FIG.16). A stabilizing plate 94 is attached to the end of this rod 92. Theplate 94 is contoured to match the curvature of the I-Patch device 28,which in turn is contoured to match the curvature of the spinal cord SC.The I-Patch main assembly contains the transceiver antenna and controlcircuitry and fits snuggly into IPA stabilizing plate 94.

The I-Patch flexible attachment arms 36 extend away from the mainassembly and are contoured to follow the curvature of the spinal cordsurface S. The distal ends of these flexible arms 36 can be reversiblyextended during the insertion procedure in order for the I-Patch to beplaced oh the spinal cord SC. This function is achieved by securing asuture through an eyelet 96 positioned at the termination points of theflexible arms 36. A double strand suture 98 is then passed through aseries of islets 100 until secured to a suture tension adjustment rodhaving a knob 102. The surgeon rotates this rod to adjust theconformation of the extension arms. When the I-Patch is being insertedonto the spinal cord, the adjustment rod is rotated into a position thatachieves the desired degree of flexible arm extension. Once the I-Patchis in the desired position, the surgeon rotates the adjustment rod untilthe flexible arms have returned to their pre-formed position, resultingin uniform, gentle, direct contact of the entire I-Patch device with thespinal cord surface. The surgeon then disengages the IPA from theI-Patch by cutting the tension sutures. The cut sutures are gentlyremoved, followed by removal of the IPA. The entire insertion procedureshould be accomplished in approximately 15 seconds (FIG. 17).

The I-Patch system will typically include a thin-film extra-dural device40 that wirelessly transmits power and command signals to the spinalcord electrode assembly 28 This extra-dural device element 40 achievesthe following design goals. Optionally, no physical connection betweenthe power/command relay device and the spinal cord electrode (i.e. no‘tethering’). No physical obstruction of the CSF surrounding the spinalcord (avoid risk of syrinx formation). Optionally, no device elementspenetrate the dura in a manner that would result in an increased risk ofCSF fistula formation. The distance, or gap, across which wirelesstransmission occurs can be made be as short as possible withoutcompromising the other device design specifications.

The extradural relay device 40, however, will be exposed to bloodproducts/plasma serum that always accumulates in the extra-dural spacefollowing surgery. In some instances, these materials could accumulatein the space between the extra-dural device and dura, altering thespatial and electromagnetic relationships between the relay device andthe spinal cord implant. While this will not usually be a concern, undercertain circumstances the electromagnetic coupling between theextra-dural and spinal cord elements may be affected, as it is highlysensitive to relative spatial relationships and the dielectricproperties of intervening materials.

An intra-dural relay device (IDRD) 120 as may be used an alternative tothe extra-dural relay element 40 and may have superior performancecharacteristics under certain circumstances. The IDRD 120 includes athin film power/command relay device body 122 that is placed on theinner surface of the dura lining the dorsal aspect of the spinal canalSee FIGS. 18 through 21. The pliable thin film device 122 contours tothe curved surface of the dorsal spinal canal dura and is held in placewith sutures 124. It is placed after the spinal cord electrode arraydevice 28 is positioned, at the beginning of the dural closureprocedure. The doral closure procedure does not differ significantlyfrom the standard closure procedure. The risk of CSF leak around thelead cable emanating from the thin film IDRD is eliminated by using asimple ‘washer’ clamping method at the lead cable exit site. Followingsurgery, the IDRD body 122 will lay flush with the inner surface of thedura. The IDRD's low profile will not obstruct CSF flow. The spatialrelationship between the IDRD and spinal cord electrode away will not bealtered by the post-operative accumulation of blood products in theextra-doral space. The surgical technique fur suturing closed the durawill not differ significantly from that used with the ‘standard’ I-Patchprocedure. Only additional seconds are required to place the ‘washer’and crimping device, such as by sliding a dual compression washer 126along a flexible lead 128 beyond a groove 130 so as to secure the washerin position by a clamping or washer compression device 140, with thedura clamped between the washer 126 and a flanged, flat backstop 132 ofIDRD body 122. The IDRD 120 can be secured in position under the surfaceof dura 10 within cut dura edges 134 with stay sutures 136 placed atproximal and distal ends of the IDRD body 122. Dural edges 134 can beapproximated by sutures 138, and washer 126 can then be slid along lead128 beyond groove 130 so that the crimp or washer compression device 140engages the groove.

FIGS. 22 and 23 show one embodiment of the electronic elements thatmight be on-board the I-Patch spinal cord implant. FIG. 22 shows thetransceiver coils that inductively couple power and information signalsinto the circuit. A bridge circuit converts the ac signals to de voltagelevels, in order to provide power to the rest of the circuit. A resetsignal is generated from the input pulses via a Schmitt trigger. FIG. 23shows the other elements of the control and pulsing circuit. Theseconsist of a phase-locked-loop that generates a pulse train which isoperated on by a counter, and a 3-bit to 8-line decoder that, with amonostable multivibrator, converts the counter's wavetrain into signalsthat are distributed to selected electrodes. The above-mentioned resetsignals are used to clear the circuit elements at the end of eachpulsing cycle.

FIG. 24 shows the somatotopical organization of the dorsal spinal columnaxons. Embodiments of the devices, systems, and methods described hereinmay make use of such organization by selectively energizing electrodesof the array structure 28 so as to inhibit focal pain of (or otherwisetreat) somototopically corresponding anatomy of the patient. Axialregions T11, T12, L1, and L2 are associated with low back signals; L3,L4, and L5 are associated with leg and foot signals 152; and S1-S4 areassociated with pelvis signals 154; so that stimuli applied to one ofthese regions may provide therapeutic effects for pain of the associatedanatomy. Note that limiting lateral transmission of stimuli by employingdirect contact or near field signal transmission from a discreteelectrode of the array to the spinal cord may be particularly beneficialfor treatment of low back pain or the like, as the axons associated withlow back pain may be located in close proximity to the dorsal root entryzone DREZ, and inhibiting transmission of spurious or collateral signalsto the DREZ may improve the efficacy and/or decrease deleterious effectsof the therapy.

FIGS. 25 and 25A show dentate ligament structures that extend laterallybetween the spinal cord and surrounding dura. More specifically, FIG. 25is a profile-view diagrammatic representation of the human spinal cordwith surrounding meninges. Arachnoid mater A is closely applied to thethick outer dura 10. An intermediate leptomeningeal layer IL liesbetween the arachnoid mater A and the pia mater. This layer isfenestrated and is attached to the inner aspect of this arachnoid mater.It is reflected to form the dorsal septum S. Dentate ligaments 160 arepresent on either side of the spinal cord SC. The collagenous core ofthe dentate ligaments fuses with subpial collagen medially and atintervals laterally with dural collagen, as shown on the left side ofthe diagram. Blood vessels V within the subarachnoid space are seenalong a surface of the spinal cord SC. As cart be seen in the axialsection through the spinal cord of FIG. 25A, dorsal rootlets 162 andventral rootlets 164 may extend from spinal column SC dorsally andventrally of denticulate ligaments 160, with the dentate ligamentsgenerally attaching the left and right lateral portion of the spinalcord SC to left and right regions along an internal surface of dura 10.Additional details regarding these anatomical structures may beunderstood, for example, with reference to “The Fine Anatomy of dm HumanSpinal Meninges” by David S. Nicholas et al.; J. Neurosurg 69:276-282(1988); and to “The Denticulate Ligament: Anatomy and functionalSignificance” by R. Shane Tubbs et al.; J. Neurosurg 94:271-275 (2001).

FIGS. 26 and 26A show yet another alternative embodiment of an I-Patch170 having an electrode array 34 supported by a body 172 including aflexible substrate or backing as described above, with the array hereconfigured to engage a dorsal portion of the spinal cord SC. Dentateligament attachment features such as flexible arms 174 extend laterallyfrom left and right sides of body 172, with the arms optionallycomprising the same substrate or backing material from which the body isformed. These arms or other features are configured to be attached toleft and right dentate ligaments 160 on either side of the treatmentregion of the spinal cord so as to support the array 34 in engagementwith the surface of the spinal cord.

The dentate ligament provides a thin, but high tensile strength fibrousattachment that extends from the lateral spinal canal wall to fuse withand attach to the pia-arachnoid membrane on the lateral surface of thespinal cord, approximately at the ‘equator’ of the cord as viewed incross-section. This location and geometry is well suited for gentlyexerting a desirable amount of downward/inward pressure on the I-Patch,optionally without having to resort to sutures and without using any‘non-targeted’ parts of the spinal cord as points of attachment. Thebody of dentate-ligament supported I-Patch device 170 may be largely orentirely flexible and/or elastic. Electrodes 34 may be arrayed toprovide coverage within the dorsal column of the spinal cord and may beembedded in a flexible silicone-type, biocompatible material. Thedentate ligament attachment features such as attachment arms 174 may bemore highly elastic, optionally having no electronic elements containedwithin them, and may extend laterally from the electrode-bearing bodyportion of the device. These attachment arms can be thin (optionallybeing thinner than the substrate adjacent the electrode array), flat,and/or floppy. The attachment arms may ‘flair’ to a larger widthadjacent the ends opposite the array, and/or may have slightly raisedgroves or texture at or near these ends to facilitate clipping,crimping, and/or adhesively bonding the arms to the dentate ligament.

During implantation, the dentate ligament supported I-Patch device 170may be placed and centered over the exposed dorsal column of the spinalcord. A small number of rootlets may optionally be sectioned to createroom for the attachment arms (as may also be done with other I-Patchembodiments). The flared end of each attachment arm can be draped on thedentate ligaments on either side of the spinal cord. With the patient inthe prone position the gravitational forces will result in a gentle fitof the electrode bearing portion of the I-Patch on the dorsal spinalcord. The amount of downward gravitational force exerted on the I-Patchwill not be large enough to occlude surface blood vessels. The preferredpoints of contact will be between an array of slightly protrudingelectrode contacts and the pial surface of the dorsal columns.Microchips 176 or other types of fixation or crimping devices can beused to secure the attachment arms to the dentate ligaments. Metalmicroclips used in a variety of surgeries (e.g. Week Clips) may beemployed, though non-metallic clips or other fasteners may haveparticular advantages, and are used widely for endoscopic surgicalprocedures. A relatively broad surface of attachment is beneficialbecause of the thin, almost spider web nature of the dentate ligament.An approximately 3 mm clip may, for example, be employed. Alternatively,a tissue glue could be used. With many techniques, there is norequirement for the I-Patch, or I-Patch attachment arms to be jostled ormanipulated into position. The device is simply draped on the dorsalspinal cord surface and dentate ligaments, and secured in place. Withthese embodiments, the ‘point of attachment’ or ‘anchor point’ of thedevice may be on connective tissue rather than spinal cord tissue,limiting the clinical significance of any damage to the supportingtissue structure.

A variety of alternative dentate ligament-supported I-Patch embodimentsmay be provided, including embodiment 190 of FIGS. 27 and 27A. Ingeneral, these embodiments of the I-Patch should be highly flexible soas to avoid restricting normal spinal cord pulsations in-situ. Firm,constant mechanical contact should be achieved between the electrodesurfaces and the pial surface of the spinal cord. A ‘cue size fits’ alldesign is desirable, whereby a standard device can accommodate almostthe full range of spinal cord anatomy variants encountered in patients,and/or where a limited number of sizes (1-5) will span a significantpatient population. The implantation procedure should be simple, safe,last and un-complicated. Toward that end, embodiment 190 makes use ofthe dentate ligaments 160 to serve as a purchase point for a malleableI-Patch electrode array. There is a simple clasp 192 at the end of eachmalleable or plastically deformable I-Patch attachment arm 194. In theoperating room, the surgeon secures the ends of each attachment arm 194to the dentate ligaments 160. These ligaments are comprised ofconnective tissue and have no innervation. They are firmly attached tothe lateral margin of the spinal cord. The highly elastic/malleableI-Patch electrode assembly 190 is thus secured to the spinal cordsurface. Advantages of this and/or other dentate ligament supportedI-Patch variants may include a relatively simple electrode design. Also,these embodiments should result in excellent mechanical contact betweenelectrodes and pial surface, as the dentate ligaments will easilywithstand the chronic forces exerted on them by the I-Patch. Thevariability provided through deformable arms may allow a ‘one size fitsall’ (or limited number of sizes) in the device, and the implantationprocedure may be relatively less complicated. Penetrating electrodes mayoptionally be employed in place of the contact electrodes, with the bodyof many of the dentate ligament embodiments optionally providing a pialsurface platform to which such electrodes could be mounted.

FIG. 28-28F illustrate a still further ‘wired’ alternative dentateligament (DL) supported embodiment of an I-Patch 200, along withimplantation of that device so that a lead extends along (and isattached to) one of the dentate ligaments and is sealed where it extendsthrough the dura. Wired DL I-Patch 200 has a flexible lead that extendsthrough dura 10, with the lead preferably extending along one of the DLattachment arm 174. The lead then optionally runs laterally anddorsally, hugging the inner surface of the dura 10, optionally using astaple, clip, suture, or stapled bracket 210 to maintain the position ofthe lead against the dura. The lead 202 may exit the dura 210 along themidline. By placing crimping clips 176 to secure the lead hearingI-Patch attachment arm 174 to the DL 160, a strain relieving functionwill be achieved. This should prevent torquing on the I-Patch by theleads and injury to the spinal cord with spinal cord movement. As shownin FIGS. 28B-28F, a dura-traversing lead fitting 212 can help inhibitlead migration and facilitate water-tight dural closure, with the leadoptionally being disposed along a re-approximated mid-line durotomyafter closing most of the incision using standard techniques. Acompression clip 216 can engage fitting 214 to help seal the doralleaflets to each other around fitting 214, and tissue glue 218 can alsobe placed on and around the compression clip to effect closure.

FIG. 29 schematically illustrates an electrode extending from aninterior surface of a backing or substrate of an array structure of theI-Patch. The therapeutic benefit of the I-Patch to the patient may beenhanced by maximizing the SCS current densities in the targetedconducting tracts of the spinal cord itself, while minimizing thecurrent density shunted away by the CSF. This benefit may be enhanced byengaging the electrodes against the surface of the spinal cord as shown,with a stand-off column 220 extending between the exposed portion of theelectrode 34 and the underside of the implant substrate body 222. Thiscan support the implant off the surface S of the spinal cord SC by about100 μm to accommodate micropulsations of the spinal cord, as describedabove. By insulating the surface of stand-off column 220, it is possibleto minimize the shunting effect of the CSF, as the exposed portion ofthe electrode will be in contact only with the pial surface of thespinal cord, and not with the CSF itself. Gentle inward pressure causesslight inward “dimpling” of the pial surface by the electrode. As aresult, the un-insulated (active) exposed surface of the electrode is“sealed” by spinal cord tissue enveloping the protruding portion of thecontact. A small gap separates the electrically inactive portions of theI-Patch device, providing space into which the spinal cord tissue mayexpand and contract with cardiac pulsation cycles.

FIG. 30 schematically illustrates individual electrodes 34 flexiblymounted to a backing or substrate 230 by a soft resilient material 232so as to allow the electrode to resiliently float or move radiallyand/or laterally relative to the substrate by a distance that is atleast as large as the pulsations of the surface S of spinal column SC.This movement of the individual electrodes may inhibit slidingengagement of the electrodes against the surface of the spinal cordduring pulsation. In some implementations of the I-Patch the only partsof the I-Patch device that directly engage the spinal cord are theelectrode contacts. These may serve as mechanical anchoring points forthe device. They should exert just enough pressure to maintain goodelectrical contact with the surface of the spinal cord. The pressureexerted on the spinal cord by the contacts should be generally even forall of the contacts. Some embodiments achieve this by having electrodesprotruding slightly from contoured attachments arms. These contouredattachment arms position all contacts in the desired position relativeto the surface of the spinal cord. Outward and inward movements of thecontacts (e.g. with pulsations and respirations) are accommodated bymovements of the semi-rigid attachment arms. Unfortunately, this makessignificant demands on the mechanical characteristics of the attachmentarms. The arms may benefit from being contoured to a spinal cord ofindividual patients, and they should be constructed of materials thatboth bold this contour for a decade or more, yet expand and contract toaccommodate spinal cord expansion/contraction.

The mobile electrode approach facilitates design and materialperformance goals of the attachment arms. Each contact is mobile andattached to the I-Patch via an elastic/spring-like interface. The degreeto which each contact extends out from the attachment arm is determinedby the distance separating the attachment arm from the spinal cordsurface at each contact location. The elastic nature of the connectionbetween each contact and the attachment arm/body cause each contact toindependently protrude out from the device until the desired tissuecontact/force interface is achieved. In this way desirable mechanical;interfaces are achieved between some, most, or all electrode contactsand the spinal cord, even if the attachment arms/body do not conformperfectly to the shape of the spinal cord. Also, the elastic interfaceallows the contacts to slide in and out with expansion/contraction ofthe spinal cord without attachment arm movement. With mobile contacts,the attachment arms can be more rigid and will not be required toperfectly follow the contour of each patient's spinal cord.

In the embodiment of FIG. 30, electrode bodies 234 extend throughapertures 238 in substrate 230, with the substrate being pliable andhaving elasticity appropriate to supporting thin film circuitcomponents. A soft elastomeric material 236 spans the apertures fromsubstrate 230 to the electrode bodies, with the elastomeric materialhere comprising a sheet of material adhered to the outer surface of thesubstrate. In other embodiments, the electrodes may be supportedrelative to each other and the substrate with a soft elastomericmaterial spanning directly between the electrode and walls of theaperture (such as by insert molding the material into the apertures withthe electrode bodies positioned therein). In still further alternativeembodiments, the resilient material may form column 220 or the like.Flexible conductors (not shown) may extend between the substrate andelectrode bodies within or outside the elastic material with theseconductors optionally being serpentine, having loops, or the like toaccommodate movement of each electrode body relative to the substrate.

As can generally be understood from the description and the parentprovisional application, embodiments of the invention provide animplantable electronic system including and/or consisting of a signalgenerator means and a signal transceiver means. The transceiver meansconforms to a surface structure of a region of spinal cord in a patient.The transceiver means is able to receive signals wirelessly from saidsignal generator means, and to process said signals according to analgorithm. The algorithm is then able to cause said transceiver means togenerate electrical stimuli according to said algorithm. Said stimulican be applied by electrodes of said transceiver means to selectedpoints on the surface of said spinal cord in said patient.

Optionally, the transceiver means may include and/or consists of anelectronic circuit, a pliable substrate containing said electroniccircuit, a plurality of contact points that apply said stimuli from saidcircuit to said spinal cord, and attachment arms that hold said pliablesubstrate in non-damaging contact with said spinal cord.

In some embodiments, said generator of said wireless signals consists ofa signal production means and an inductive coupling means such as aplanar coil prepared on the surface of a pliable substrate. In someembodiments, said planar coil of said signal generator means isconfigured and positioned so as to conform to the inner or outer surfaceof a region of the dura mater surrounding the spinal cord. In someembodiments, said planar coil of said signal generator means deployed ona region of said dura mater of said spinal cord and said transceivermeans deployed on the actual surface of said region of said spinal cordare positioned in proximity to each other and separated only by thethickness of said dura mater itself and/or by the layer of cerebrospinalfluid filling the gap between said inside surface of said dura mater andsaid outer surface of said transceiver means which is in intimatecontact with said region of spinal cord.

In some embodiments, said planar coil of said signal generator meanscommunicates inductively with an opposing coil that is part of saidelectronic circuit means on said transceiver means in order to transferelectrical power and electrical control signals from said generatormeans to said transceiver means, as in an electromagnetic transformer.In some embodiments, said electronic circuit on said transceiver meansfurther consists of circuit elements that may include an informationprocessing means, a memory means, a bus means, a signal distributionmeans and other means for executing the function of the device accordingto the method of the invention. In some embodiments, said informationprocessing means of said transceiver means is able to execute one of aplurality of algorithms that are resident either within said memorymeans of said transceiver or within said generator, with said algorithmbeing chosen in response to the physiological and anatomical needs ofsaid patient.

The electrical stimuli produced by said transceiver means in response tothe action of said algorithm means can be applied to selected points onsaid region of spinal cord of said patient in response to thephysiological and anatomical needs of said patient The electricalstimuli produced by said transceiver means arc generated as desired forthe treatment of intractable pain as might be caused by musculo-skeletaldisorders, neoplasms, arthritic degenerations, neurodegenerativedisorders, trauma and/or the like.

The circuit of said transceiver may include an assembly of discrete orintegrated analog and digital components. The analog circuit elementswithin said transceiver may include active and passive components. Thedigital circuit elements within said transceiver may operate onelectronic pulses, analog or digitized waveforms, dc voltage levels,and/or combinations thereof. The electronic circuit for said transceivermay incorporate a signal multiplexer that is able to distribute aplurality of stimulus signals to a plurality of electrodes in contactwith a spinal cord of a patient. The electronic circuit for saidtransceiver may incorporate a phase-locked-loop system for detecting,synthesizing or processing a plurality of electronic waveforms, pulsesand combinations thereof, for subsequent use in generating anddistributing stimulus signals to a plurality of electrodes in contactwith a spinal cord of a patient. The electronic circuit for saidtransceiver may incorporate frequency-shift keying and/or pulse-widthmodulation means for detecting, synthesizing or processing a pluralityof electronic waveforms, pulses and combinations thereof for subsequentuse in generating and distributing stimulus signals to a plurality ofelectrodes in contact with a spinal cord of a patient. The electroniccircuit for said transceiver may contain subcircuits to preventaccidental delivery of excess voltages to the spinal cord of a patientduring the normal application of stimulus signals. The electroniccircuit for said transceiver may contain ferrite elements to prevent thepropagation within the circuit of parasitic or spurious radio-frequencysignal components. The electronic circuit for said transceiver means maycontain miniature solid-state fuses, fusible links or other such currentinterrupters, as well as back-up circuits, to protect said transceiverand said spinal cord of said patient from short circuits or other modesof failure. The electronic circuit for said transceiver may containcapacitive or inductive energy storage to allow for uninterruptedsynthesis and application of stimulus signals in the event ofinterruption of the power transfer process.

While exemplary embodiments of the devices, systems, and methods havebeen described in some detail for clarity of understanding and by way ofexample, a variety of changes, modifications, and adaptations will beobvious to those of skill in the art. Hence, the scope of the inventionis limited solely by the appended claims.

The invention claimed is:
 1. A method of intradurally implanting anelectrode assembly in a subject against the spinal cord, comprising: (a)surgically preparing the subject by exposing the dura that surrounds thesubject's spinal cord; (b) making an opening in the dura; (c) insertingthe electrode assembly though the opening so that a plurality ofelectrodes on the electrode assembly are placed in direct contact withthe surface of the spinal cord at a treatment site inside the dura; (d)securing the electrode assembly such that the electrodes stay in placeand the cerebrospinal fluid (CSF) filled space is maintained, therebysustaining direct contact between the plurality of electrodes and thesurface of the spinal cord at the treatment site while allowing CSF toflow between the electrode assembly and the dura; and (e) surgicallyclosing the dura around the electrode assembly.
 2. The method of claim1, whereby the electrode assembly is secured against the spinal cord atthe treatment site such that the electrodes exert generally evenpressure on the spinal cord, thereby serving as mechanical anchoringpoints for the electrode assembly.
 3. The method of claim 1, whereby theelectrode assembly is secured against the spinal cord at the treatmentsite such that each electrode can move independently in relation to theassembly, thereby accommodating pulsations of the surface of the spinalcord.
 4. The method of claim 1, which comprises wrapping flexibleattachment arms that extend from either side of the backing around thespinal cord.
 5. The method of claim 4, which comprises implanting atransmitter outside the dura; and wirelessly connecting the transmitterwith a receiver circuit in the electrode assembly, thereby configuringthe transmitter for wireless transmission of energy to the electrodeassembly.
 6. The method of claim 1, which comprises extending conductorselectronically connected with the electrodes out through the dura; andclosing the dura around the conductors so as to form a water-tightclosure.
 7. The method of claim 6, whereby the conductors pass from theelectrodes to the surrounding dura at positions that are adjacent toleft and right dentate ligaments.
 8. The method of claim 6, furthercomprising electronically connecting the connectors to a power supplybattery and a control circuit that have been implanted subcutaneously inthe subject.
 9. A method of stimulating the spinal cord in a subject inneed thereof, comprising delivering electrical stimulation to the spinalcord of the subject by way of an electrode assembly that has beenimplanted inside the dura and against the spinal cord of the subjectaccording to the method of claim
 1. 10. The method of claim 9, whereinthe electrodes are activated selectively so as to stimulate thesubject's spinal cord in a preprogrammed spatio-temporal sequence.
 11. Amethod for treating back pain in a subject, comprising stimulating thespinal cord of the subject according to the method of claim
 9. 12. Amethod of intradurally implanting an electrode assembly in a subjectagainst the spinal cord, comprising: (a) surgically preparing thesubject by exposing the dura that surrounds the subject's spinal cord;(b) making an opening in the dura; (c) inserting the electrode assemblythough the opening so that a plurality of electrodes on the electrodeassembly are placed in direct contact with the surface of the spinalcord at a treatment site inside the dura; (d) securing the electrodeassembly such that the electrodes stay in place without constricting thedura to the spinal cord, thereby sustaining direct contact between theplurality of electrodes and the surface of the spinal cord at thetreatment site while accommodating normal movement of the spinal cordwithin the spinal canal; and (e) surgically closing the dura around theelectrode assembly.